Quote:
Originally posted by pigglet
Hmmm...I may be really late, but these questions always bug me. I get something different from you Artsemis for #1. My reasoning is as follows :
if W = integral(f*dx) and f = -k*x, the W = int[-k*x*dx]. If you integrate that from 0 -> 6, you get W = -k*x^2/2, and apply limits of integration and all that, and you can back out k. Integrating the second one gives you something different from 216 for the W for a foot...but I'm curious about the answer when you get it back. Good luck.
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W = -k*x^2/2 is correct. Now plug in 6 for the upper limit to get W = -k*36/2 = -k*18. Since W = 54 was given, we have 54 = -k*18, so k = -3.
Now all you have to do is integrate from 0 to 12 of -kx dx, which is 3x dx.
That help?
And for those that were wondering. I got full credit, but yes, my units were off. The correct answers were:
1) 216
2) 53,125